JPH05234850A - Projecton aligner and manufacture of semiconductor device by using the same - Google Patents

Abstract

PURPOSE:To obtain a projection aligner wherein it constitutes a multifocal system, its depth of focus is increased and it can obtain a high-resolution projec tion pattern and to obtain the manufacturing method, of a semiconductor device, which uses it. CONSTITUTION:A circuit pattern on the face of a first object 2 is irradiated with a light flux from an irradiation system 1; the circuit pattern on the face of the first object is projected and exposed on the face of a second object 5 by using a projection optical system 3. At this time, two crystal optical elements 4 whose optical axes are crossed at right angles to each other are arranged in a light path between the first object and the second object; a diaphragm 7 provided with a cross-shaped opening is arranged near the pupil of the projection optical system in such a way that the direction of the opening is directed to the direction of the optical axis of the crystal optical elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus and a semiconductor device manufacturing method using the same, and more specifically, a circuit pattern on a reticle surface in a so-called stepper which is a semiconductor element (semiconductor device) manufacturing apparatus. The focal depth of the projection optical system is expanded so that projection can be performed on the wafer surface with high optical performance.

[0002]

2. Description of the Related Art The recent progress in manufacturing technology of semiconductor devices is remarkable, and accompanying it, the progress of fine processing technology is remarkable.
In particular, the optical processing technology has reached the level of fine processing technology having submicron resolution at the border of the production of semiconductor devices of 1M DRAM. In many cases, a method of fixing the exposure wavelength and increasing the NA (numerical aperture) of the optical system has been used as a means for improving the resolution. However, recently, various attempts have been made to change the exposure wavelength from g-line to i-line and improve the resolution by an exposure method using an ultra-high pressure mercury lamp.

Along with the development of the method of using g-line or i-line as the exposure wavelength, the resist process has also developed. The combination of this optical system and the process has led to rapid advances in optical lithography.

It is generally known that the depth of focus of a stepper is inversely proportional to the square of NA of the projection optical system. Therefore, when trying to obtain submicron resolution, the problem arises that the depth of focus becomes shallower with it.

On the other hand, various methods have been proposed for improving the resolution by using light having a shorter wavelength, which is represented by an excimer laser. It is generally known that the effect of using light of a short wavelength has an effect that the depth of focus is inversely proportional to the wavelength, and the shorter the wavelength is, the deeper the depth of focus becomes.

In addition to the use of light with a short wavelength, various methods using a phase shift mask (phase shift method) have been proposed as methods for improving resolution. This method is intended to improve the resolution by forming a thin film on a part of a conventional mask that gives a phase difference of 180 degrees with respect to the passing light with respect to the other part. Levenson
Proposed by et al. The resolving power RP is generally represented by the equation RP = k ₁ λ / NA, where λ is the wavelength, k _{1 is} the parameter, and NA is the numerical aperture. It is known that the parameter k ₁ , which is usually in the practical range of 0.7 to 0.8, can be greatly improved to about 0.35 by the phase shift method.

Various types of phase shift methods are known, for example, Nikkei Microdevice 1990 7
It is described in detail in Fukuda et al.'S papers starting on page 108 of the monthly issue.

The above-mentioned imaging method represented by the phase shift has a problem that it can be applied only to a periodic pattern having repetitions. Therefore, the effect on the image formation of an isolated so-called isolated pattern such as a contact hole, which is the most problematic, cannot be expected. Another imaging method is required as an imaging method for an isolated pattern. A so-called FLEX method is known as a method for extending the depth of focus of an isolated pattern. This method is to form a multiple image in the optical axis direction of the projection optical system, expose it, and superimpose it to extend the depth of focus of the isolated pattern as a whole.

As described above, the light exposure method is required to adopt a separate image forming method in consideration of the peculiarity of the pattern.

[0010]

In the conventional FLEX method, multiple exposure is performed by moving a wafer to be exposed along the optical axis direction of an imaging system (projection optical system) for projecting and forming a pattern. The depth of focus of the imaging system is extended while maintaining the resolution. However, this method has a problem that a member must be moved to perform multiple exposures and that the shutter must be opened many times, and that exposure takes time.

As another method, there is also a method of forming and combining a multiple image by a plurality of optical systems, or a method of forming a multiple focus system by inserting a phase type filter in the pupil plane of the projection exposure optical system. However, it is difficult to synthesize a plurality of optical systems with this type of ultra-precision optical system, and it is difficult to create a method using a phase-type filter, and at the same time, high-order diffracted light emerges and adversely affects imaging. There is a problem of giving.

According to the present invention, the multifocal optical system is constructed so that it can be performed by one exposure without moving the object to be exposed at the time of exposure. It is an object of the present invention to provide a projection exposure apparatus and a method for manufacturing a semiconductor device using the projection exposure apparatus, which can easily obtain a projection pattern image having a deep depth of focus and a high optical performance by constructing without any damage.

[0013]

In order to achieve the above-mentioned object, the present invention comprises a crystal optical element in the projection optical system as means for constructing a multifocal optical system, and the telecentricity of the projection optical system and the combination of the crystal optical element are combined. It is characterized by utilizing refraction. If a crystal optical element is inserted and the imaging effect becomes complicated due to birefringence, a component that adversely affects the imaging effect is cut, so an amplitude type filter is inserted in the pupil plane of the projection optical system. I am trying. Unlike the phase type, the amplitude type filter is easy to make because it only needs to block light, and can be easily applied to the conventional projection optical system. Further, even when a pattern other than an isolated pattern is imaged, the amplitude type filter and the crystal optical element can be easily exchanged according to the configuration of the present invention, so that an image-forming system with mobility that matches the characteristics of the pattern is configured. What is possible is also a feature of the present invention.

The structure of the projection exposure apparatus of the present invention is as follows: (a) The circuit pattern on the first object plane is illuminated by the light flux from the illumination system, and the circuit pattern on the first object plane is projected by the second object by the projection optical system. When projecting and exposing on a plane, two crystal optical elements whose optical axes are orthogonal to each other are arranged in the optical path between the first object and the second object, and a cross shape is provided in the vicinity of the pupil plane of the projection optical system. It is characterized in that a stop having a circular aperture is arranged such that the aperture direction is oriented in the optical axis direction of the crystal optical element.

In particular, the direction of the optical axis of the crystal optical element and the direction of the cross-shaped aperture of the diaphragm coincide with the main direction of the circuit pattern on the first object plane, and the projection optical system has the first direction. The two object side is composed of a telecentric system, and the two crystal optical elements are provided in the telecentric system.

(B) When the circuit pattern on the first object plane is illuminated by the light beam from the illumination system and the circuit pattern on the first object plane is projected and exposed on the second object plane by the projection optical system, First
A crystal optical element is arranged in the optical path between the object and the second object with its optical axis substantially aligned with the optical axis direction of the projection optical system,
A feature is that a double focal point is formed in the optical axis direction of the projection optical system.

(C) A projection optical system for projecting the pattern of the mask onto the wafer and the main of each imaging light beam for imaging the pattern so that the pattern is imaged at a plurality of positions in the optical axis direction of the projection optical system. And a birefringent member arranged at a position where the light beam is substantially parallel to the optical axis of the projection optical system.

Particularly, the birefringent member is provided so as to be retractable from the place, or the birefringent member is provided with a single crystal plate, and the direction of the optical axis of the crystal plate is aligned with the direction of the optical axis. That is, the birefringent member is provided with first and second crystal plates, and the optical axes of the first and second crystal plates are set to lie in planes orthogonal to each other and to the optical axis. That is, a filter for blocking light entering or passing through a portion corresponding to each quadrant when xy coordinates are set with the optical axis as the center and the directions of the optical axes as the x and y directions are set. The feature is that they are arranged.

The semiconductor device manufacturing method of the present invention includes: (d) a circuit pattern on the reticle surface illuminated by the light flux from the illumination system is projected and exposed on the wafer surface by the projection optical system, and the development processing step is performed. Then, when manufacturing a semiconductor device, two crystal optical elements whose optical axes are orthogonal to each other are arranged in the optical path between the reticle and the wafer, and a cross shape is formed near the pupil plane of the projection optical system. It is characterized in that the stop having the aperture is arranged so that its aperture direction is oriented in the optical axis direction of the crystal optical element.

In particular, the optical axis direction of the crystal optical element and the cross-shaped opening direction of the diaphragm coincide with the main direction of the circuit pattern on the reticle surface, and the projection optical system is telecentric on the wafer side. Consists of a system
The two crystal optical elements are characterized in that they are provided in the telecentric system.

(E) The circuit pattern on the reticle surface illuminated by the light flux from the illumination system is projected and exposed on the wafer surface by the projection optical system, and when the semiconductor device is manufactured through the developing process, the reticle and the wafer are manufactured. A crystal optical element is disposed in the optical path between the optical axis and the optical axis of the projection optical system so as to substantially coincide with the optical axis direction of the projection optical system, and a double focal point is formed in the optical axis direction of the projection optical system. Is characterized by.

(F) A method of manufacturing a semiconductor device by projecting a circuit pattern on a wafer by a projection optical system to print the circuit pattern on the wafer and processing the wafer on which the circuit pattern is printed. In, the circuit pattern is imaged at a plurality of positions in the optical axis direction of the projection optical system at locations where the chief ray of each imaging light flux that forms the circuit pattern is substantially parallel to the optical axis of the projection optical system. It is characterized by arranging a birefringent member.

In particular, the circuit pattern is formed of an isolated pattern such as holes, the birefringent member has a single crystal plate, and the direction of the optical axis of the crystal plate is aligned with the direction of the optical axis. , The birefringent member includes first and second crystal plates, and the optical axes of the first and second crystal plates are set to be orthogonal to each other and in a plane orthogonal to the optical axis. Alternatively, a filter for blocking light incident or passing through a portion corresponding to each quadrant when xy coordinates are set with the optical axis as the center and the directions of the optical axes as the x and y axis directions are set. The feature is that they are arranged.

[0024]

The present invention provides a multi-focus optical system (double focus) by providing a crystal optical element in a projection optical system and utilizing the telecentricity of the projection optical system and the birefringence of the crystal optical element. The main feature is that

Therefore, before explaining the structure of the present invention, the behavior (propagation) of light in the crystal optical element will be described first.

FIG. 2 is a perspective view of an essential part of the crystal optical element 4 used in the present invention. The coordinate axis x as shown in FIG.
Consider yz, and consider light L23 incident on the origin 22 on the surface of the crystal optical element 4 at an angle θ. The angle formed by the projection of the incident ray on the xy plane is α. The crystal optical element 4 used in the present invention is configured by laminating two crystal optical elements (hereinafter also simply referred to as “crystals”) 4a and 4b, and each thickness is d.

The optical axis of the first crystal 4a coincides with the y-axis, the optical axis of the second crystal 4b coincides with the x-axis, and the optical axes of the two crystals 4a and 4b coincide with each other. The axes are orthogonal to each other. The refractive index of the ordinary ray of the crystal is n _o and the refractive index of the extraordinary ray is n _e .

The incident ray L23 is divided into an ordinary ray and an extraordinary ray in the crystal. The ordinary ray on the first crystal is 2
The extraordinary ray in the first crystal becomes an extraordinary ray, while the extraordinary ray in the first crystal becomes an ordinary ray in the second crystal. These two lights form two lights forming a multifocal image. 2 separated
The two lights are polarized orthogonally, and if the incident light is unpolarized, it is separated into two lights of equal intensity.

When a phase type filter is used in the prior art, high-order diffracted light is generated, but in the case of this embodiment, 2
Only kind of light is produced. Moreover, since the non-polarized light is generally used as the exposure light in the projection exposure apparatus for manufacturing a semiconductor element, the intensities of the two are equal and the control of the imaging characteristics is easy.

It is assumed that the incident light ray has passed x = 0 and y = 0, and the coordinates on the exit side are calculated. P is the point at which the extraordinary ray of light entering the first crystal leaves the second crystal.
(X _P , y _P ) Let _Q (x _Q , y _Q ) be the point at which light entering the first crystal as an ordinary ray exits the second crystal. Moreover, although it is a ray that does not actually exist, a point when an imaginary ray passing through the two crystals as an ordinary ray exits the second crystal is S (x _S , y _S ). These can be expressed as follows using the above parameters.

X _P −x _S = − (Δn / n _O ) d cosα tan θ _O y _P −y _S = (Δn / n _O ) d sinα tan θ _O x _Q −x _S = (Δn / n _O ) d cos α tan θ _O y _Q −y _S = − (Δn / n _O ) d sinα tan θ _O x _S = −2d cosα tan θ _O y _S = −2d sinα tan θ _O where θ _O is the following equation from the law of refraction of ordinary rays. It is a value derived more.

Sin θ = n _O sin θ _O Δn = n _e −n _O FIG. 3 is an explanatory diagram showing the relationship between points P, Q, and S. In the figure, the point P, azimuth α when the incident angle θ is fixed,
It is shown how Q moves with respect to point S. Since the point S follows the path of the ordinary ray, it moves on the circle corresponding to the incident angle. On the other hand, it can be seen that the points P and Q rotate around the point S while maintaining the relationship as if they were in a planetary motion.

Since the crystal optical element 21 of FIG. 2 is a plane-parallel plate and has no power on the outer surface, the passing light beam leaves the crystal plate while keeping the incident angle. The present invention is based on such a solution of the properties of the crystal plate.

FIG. 10 shows a crystal optical element 1 used in the present invention.
It is explanatory drawing of the optical effect of the other Example of 01. In the figure, the crystal optical element 101 is composed of one crystal optical element.

FIG. 13 is a sectional view of the essential parts of the crystal optical element 101.
Is. In FIG. 13, 61 is a quartz substrate and 101a is water.
It is a crystal. As shown in FIG. 10, the coordinate axes xyz
Angle to the origin 102 on the surface of the crystal optical element 101.
Consider the light L103 incident at a degree θ. Used in the present invention
A crystal optical element (hereinafter also referred to as “crystal”) 101 is shown in FIG.
Unlike the crystal optical element shown in, the optical axis of the uniaxial crystal
The directions are in a relationship in agreement with the z axis. The crystal has a thickness d
It is made of plane parallel plates, and the refractive index of ordinary rays is n ₀ , Abnormal
The refractive index of the light ray is n_e And At this time, the ray velocity of the ordinary ray
The surface is n₀ ²(X² + Y² + Z² ) = 1, and the ray velocity plane of the extraordinary ray is n_e ²(X² + Y² ) + N₀ ²z² It is represented by a spheroidal surface of = 1. Both are projection light described later
Since there is a relationship of rotation about the optical axis of the academic system, here
Is the cross section including y and z, and is related to the propagation of light in the crystal.
And illustrated. The light ray L103 incident on the crystal 101 is
It divides into two, the ordinary ray and the extraordinary ray in the crystal. These two
The light forms a double focus image.

FIG. 11 shows how a light ray passes through a crystal and forms an image. The solid line in the figure shows the image formation of a ray passing through the crystal as an ordinary ray, and the broken line shows the image formation of a ray passing through the crystal as an extraordinary ray. .. Since the crystal of FIG. 10 is a plane-parallel plate externally and has no power, the passing light ray leaves the crystal while maintaining the incident angle.

Therefore, the two separated lights are imaged at positions different from each other by the optical axis distance Δf as shown in FIG. That is, a double focus is achieved. In Figure 12, the light rays are crystals 1.
4 is an explanatory diagram showing a shift amount of an image forming position with respect to an angle θ incident on 01. FIG. As shown in the same figure, it can be seen that the image forming positions of the ordinary ray and the extraordinary ray are different, and these two rays form a double focus image. The paraxial amount of the deviation Δf of the focus position in the optical axis direction at this time is represented by Δf = (1 / n ₀ −n ₀ / n _e ² ) · d, the crystal material is quartz, and the wavelength is λ = 404. 6n
m, n ₀ = 1.55396, n _e = 1.56340
When Δf is calculated using, Δf = 0.0077 · d is obtained.

Here, it is understood that when the amount of defocus is set to 2 μm, for example, d≈0.26 mm should be set. 2 separated after passing through the crystal optical element 101
The two lights are polarized orthogonally, and if the incident light is unpolarized, it is separated into two lights of equal intensity.

When a phase type filter is used in the prior art, high-order diffracted light is generated, but in the case of this embodiment, 2
Only kind of light is produced. Moreover, since the non-polarized light is generally used as the exposure light in the projection exposure apparatus for manufacturing a semiconductor element, the intensities of the two are equal and the control of the imaging characteristics is easy. The present invention is based on the solution of such crystal properties.

Next, the structural features of the projection exposure apparatus of the present invention will be described. 1 is a schematic view of a main part of a first embodiment of a projection exposure apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes an illumination system, which has, for example, an ultrahigh pressure mercury lamp or an excimer laser as a light source, and illuminates the reticle 2 with exposure light. A circuit pattern is provided on the surface of the reticle 2.

A projection optical system (projection lens) 3 projects the circuit pattern on the surface of the reticle 2 onto the surface of the wafer 5 mounted on the wafer holding mechanism 6. The wafer 5 side of the projection optical system 3 is a telecentric system.

Reference numeral 4 denotes a crystal optical element, which is removably provided in an optical path which is a telecentric system between the projection optical system 3 and the wafer 5. The crystal optical element 4 has the structure shown in FIG.

In general, the projection optical system is configured to be a telecentric system on the wafer side so that the image position does not change even if the image is burned in a defocused state during exposure. The present embodiment is characterized in that the crystal optical element 4 is arranged between the projection optical system 3 and the wafer 5 and the telecentricity is utilized as described later.

Reference numeral 8 denotes a plane parallel plate, which has the same optical path length when the crystal optical element 4 is not used.
Instead of, the optical path length is provided so that it can be inserted and removed.
A diaphragm 7 has a cross-shaped opening diameter of width DW as shown in FIG. 5, and is provided in the vicinity of the pupil plane of the projection optical system 3 so that it can be inserted and removed. The diaphragm 7 is used when the crystal optical element 4 is used. It is used such that the cross-shaped opening direction of the diaphragm 7 and the optical axis directions of the two crystal optical elements 4a and 4b forming the crystal optical element 4 are substantially coincident with each other.

Reference numeral 9 denotes a diaphragm, which is formed of an ordinary circular aperture and is provided near the pupil plane of the projection optical system 3 so as to be replaceable with the diaphragm 7. The diaphragm 9 is used together with the plane-parallel plate 8 during normal projection exposure without using the crystal optical element 4. Reference numeral 10 denotes a switching mechanism such as a diaphragm provided in the illumination system 1, which changes illumination conditions when the crystal optical element 4 is used so that optimum illumination can be performed.

In the projection exposure apparatus shown in the figure, a focus system for detecting the position of the projection optical system 3 of the wafer 5 in the optical axis direction, a wafer drive system, and the like are also included in the apparatus as normal components. It has been incorporated.

In this embodiment, when the circuit pattern on the surface of the reticle 2 is projected and exposed on the surface of the wafer 5 by the projection optical system 3, a double focus image is formed by using the crystal optical element 4 to increase the depth of focus. A high resolution pattern image is obtained.

Next, the optical action at this time will be described. FIG. 4 shows an image formation state on the wafer 5 side after passing through the crystal optical element (crystal) 4. The solid line in the figure shows the image formation of a ray passing through the crystal 4 with only the ordinary ray which is a virtual ray. Here, for the sake of simplicity of explanation, it is assumed that the ordinary ray forms an ideal image at the point A which is an image forming point. In fact, the projection optical system for semiconductor manufacturing is highly corrected for aberrations, and it is safe to make such an assumption.

Corresponding to FIG. 2, the exit point S of the ordinary ray, which is a virtual ray, at the crystal optical element 4 corresponds to the point S in FIG. Since the actual ray passes through the first or second crystal as an extraordinary ray, the point P is outside the point S and the point Q is inside the point S in the zy cross section of FIG. In contrast,
In the xz cross section of FIG. 4B, the point Q is outside the point S and the point P
There is an inverted relationship that is inside the point S.

This situation has already been described with reference to FIG. The distance a from the point S to the points P and Q is a = (Δn / n ₀ ) d tan θ ₀ .

The light ray after leaving the crystal 4 becomes a light ray propagating at the same angle as the incident angle. Therefore, the two separated lights form images at different focal positions, that is, a double focus is achieved, as shown in FIG. The amount of the distance a corresponds to the amount of lateral aberration when the focal position of the light beam emitted from the point S is used as a reference.

If tan θ ₀ ≈sin θ / n ₀ is set in a very rough approximation, a = (Δn / n ₀ ² ) d sin θ, and this lateral aberration amount is an aberration corresponding to the defocus amount. I understand.

The fact that the image forming system is telecentric means that the principal ray, which is the center of the image forming light beam, is perpendicular to the surface of the wafer 5 after passing through the projection optical system 3.

Since the crystal optical element 4 in this embodiment is arranged between the projection optical system 3 and the wafer 5, the chief ray is incident on the crystal optical element 4 vertically. Since the vertically incident light passes vertically as it is, there is no deviation between the principal rays of the light split into two. Therefore, even if the crystal optical element 4 is inserted, the image points of the two lights do not shift in the direction perpendicular to the optical axis of the projection optical system 3. The position of the image forming point of the light divided into two only causes a deviation in the optical axis direction of the projection optical system 3.

As described above, by inserting the crystal optical element 4 as shown in FIG. 2, a double focus is achieved without affecting the magnification which is the deviation in the direction perpendicular to the optical axis direction and the distortion. be able to.

However, this double focus is not a simple one, and the shift of the focus position differs depending on the cross section, as can be seen from the inversion relationship of the focus states on the zy section and the zx section.

Therefore, the present invention is characterized in that the direction of image formation is restricted in order to deal with the problem that the amount of deviation of the image formation position differs depending on the cross section. The diaphragm 7 shown in FIG. 1 plays this role. As is well known, the integrated circuit pattern is mainly composed of vertical and horizontal patterns.
The coordinate system shown in FIG. 2 corresponds to the x and y axes.

In the present invention, the directions of the x-axis and the y-axis are defined as the main directions of the pattern. The direction of the optical axis of the crystal forming the crystal optical element 4 is arranged so as to coincide with the main direction of the integrated circuit pattern.

FIG. 5 shows the aperture shape of the diaphragm 7. The diaphragm 7 is designed to block ± 45 ° directions, and has a role of passing only the light flux near the x-axis and the y-axis. Therefore, the aperture shape of the diaphragm 7 has a cross shape constituted by a group of straight lines parallel to the x-axis and the y-axis. When the radius of the pupil of the projection optical system 3 is standardized to 1, and when the diameter of the effective light source of the illumination system 1 formed on the pupil surface is DW, the width of the light flux passing portion of the diaphragm 7 is a value near DW. Is desirable. FIG. 5 shows that the diameter DW of the effective light source is 0.3 and the width DW of the transmission part of the diaphragm 7 is also 0.3.

The image formation in the directions of ± 45 ° causes lateral displacement of the image in the actual image formation. As is clear from the relationship between points P and Q in FIG. 3, the shift of the two lights on the x-axis and the y-axis is the shift of the focus position on the image plane. However, the relationship between the point P and the point Q is reversed on the x-axis and the y-axis, and light having a positive defocus effect on the x-axis has a negative defocus effect on the y-axis. The image formation of the cross section in the direction of ± 45 ° is just in these two transitional regions, and the focus positions of the two lights match, but on the other hand, lateral shift of the image occurs as a side effect.

That is, the image formation in the directions of ± 45 ° is a double image in a direction shifted in the direction orthogonal to the optical axis of the projection optical system 3. Since the deviation of the projection optical system 3 in the optical axis direction is used in the present invention to increase the depth of focus, the image forming components in the directions of ± 45 ° are obstructive components.

Since the amount of deviation is proportional to sin θ ₀ , as is clear from the equation for obtaining the coordinates of the points P and Q, in the ± 45 ° direction like the aperture shape of the diaphragm 7 shown in FIG. If the angle spread of is limited, the deviation can be kept within the allowable range.

Therefore, the shape of the transmissive portion of the diaphragm 7 is not necessarily a straight line, but is limited when the lateral deviation exceeds an allowable value, specifically, the width becomes smaller as the distance from the center becomes smaller. In some cases it is preferred. As another method, a method of reducing σ under the illumination condition can be considered. In this case, the width of the opening can be reduced according to the condition of σ.

The shift amount of the focal position of the projection optical system can be arbitrarily controlled by the thickness d of the crystal optical element. If the crystal optical elements having several kinds of thicknesses can be replaced with each other, a shift amount according to the pattern can be generated. Further, since the double images are generated at the same time, the trouble of double exposure does not occur, so that it is possible to suppress the decrease in throughput.

In the present invention, the element having a power such as the lens which constitutes the projection optical system is fixed, so that the crystal optical element 4 and the diaphragm 7 are exchanged as shown in FIG. It is easy to return to the system configuration.

In the case of using a crystal which is most easily used as a crystal optical element, it is required to process a plate having a thin crystal thickness of the order of 0.1 mm. Therefore, in practice, it is necessary to attach the quartz plates 4a and 4b to the reinforcing member 61 having a constant thickness, such as quartz or BK7, as shown in FIG. The crystal plate and the reinforcing member are bonded by vacuum bonding. FIG. 6 shows the crystal optical element 4 thus produced.

When the crystal optical element is manufactured in this way,
In order to return to the normal projection optical system, it is necessary to replace the plane parallel plate having the same optical path length as the normal optical system including the reinforcing member for the optical system.

When the crystal optical element according to the present invention is used, there are optimum illumination conditions, and it may be necessary to change the illumination condition depending on whether the crystal optical element is inserted or not. As a method of changing the illumination condition in this case, that is, a method of changing σ, various known methods such as changing the diaphragm in the illumination system 1 by the switching mechanism 10 can be used.

FIGS. 7 and 8 are schematic views of the essential portions of Embodiments 2 and 3 of the projection exposure apparatus of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals. In Example 2 of FIG. 7, the crystal optical element 4 is inserted and attached to the reticle 2 side.

In this embodiment, the projection optical system 3 in this case is a telecentric system not only on the side of the wafer 5 but also on the side of the reticle 2 so that the image point is not displaced. As a basic relationship of image formation, the vertical magnification is the square of the horizontal magnification, and considering the normally used 1/5 times reduction system, the thickness of the crystal 4 is 2 when it is inserted on the wafer side in the first embodiment.
It can be quintupled.

As described above, when crystal is used as a crystal and the wafer side has a control of 0.1 mm order, the reticle side has a large control amount of mm order, and the process control is large. Is facilitated.

In Example 3 of FIG. 8, the crystal optical element 4 is inserted in the projection optical system 3 at a position where the chief ray is parallel to the optical axis of the projection optical system 3. When the projection optical system is telecentric on the wafer side, such a portion may appear inside the projection optical system.

The crystal optical element of the present invention can be inserted in such a place. The thickness of the crystal in this case is determined by the paraxial magnification relationship between the insertion position and the imaging position,
Generally, thicker crystals than in Example 1 are required.

7 and 8, a plane-parallel plate 8 replaceable with the crystal optical element 4 used in the present invention is prepared, but the optical thicknesses of the crystal 4 and the plane-parallel plate 8 are the same. .. Further, the direction of the cross-shaped opening of the diaphragm 7 and the direction of the optical axis of the crystal 4 coincide with the main direction of the pattern on the reticle 2, which is also the same as the first embodiment.

In the present embodiment, in the actual exposure, the pattern information is entered from the console of the projection optical system 3 to instruct the type and presence / absence of insertion of the crystal optical element and the type and presence / absence of insertion of the diaphragm 7. The elements are automatically set up. The same applies to the illumination conditions.

In the present invention, the image forming characteristics of the optical system can be changed without impairing the features of the projection optical system to increase the depth of the optical system for an isolated pattern such as a contact hole. Great effect.

FIGS. 9, 14, and 15 are schematic views of the essential portions of Embodiments 4, 5, and 6 of the projection exposure apparatus of the present invention. In Examples 4, 5 and 6, compared with Example 1 of FIG. 1, a crystal optical element 101 shown in FIG.
Is largely different, and other configurations are substantially the same.

Next, the structure of the fourth embodiment shown in FIG. 9 will be described although it partially overlaps with that of the first embodiment shown in FIG. Reference numeral 1 in the figure denotes an illumination system, which has, for example, an ultrahigh pressure mercury lamp or an excimer laser as a light source, and illuminates the reticle 2 with exposure light. A circuit pattern is provided on the surface of the reticle 2.

A projection optical system (projection lens) 3 projects the circuit pattern on the surface of the reticle 2 onto the surface of the wafer 5 mounted on the wafer holding mechanism 6. The wafer 5 side of the projection optical system 3 is a telecentric system.

Reference numeral 101 denotes a crystal optical element, which is removably provided in the optical path which is a telecentric system between the projection optical system 3 and the wafer 5. The crystal optical element 101 has the configuration shown in FIG. Generally, the projection optical system is configured to be a telecentric system on the wafer side so that the position of the image does not change even if the image is burned in a defocused state during exposure.

This embodiment is characterized in that the crystal optical element 101 is arranged between the projection optical system 3 and the wafer 5 and the telecentricity is utilized, as in the first embodiment.

Reference numeral 8 denotes a plane parallel plate, which is a crystal optical element 10.
In order to make the optical path length the same when not using 1, the crystal optical element 101 is provided so that it can be inserted into and removed from the optical path length. Reference numeral 10 denotes a switching mechanism such as a diaphragm provided in the illumination system 1, which changes illumination conditions when the crystal optical element 101 is used so that optimum illumination can be performed. As in the first embodiment, the projection exposure apparatus shown in the figure includes, as other normal components, a focus system for detecting the position of the projection optical system 3 of the wafer 5 in the optical axis direction, a wafer drive system, and the like. Built into the device.

In this embodiment, when the projection optical system 3 projects and exposes the circuit pattern on the surface of the reticle 2 onto the surface of the wafer 5, a double focus image is formed by using the crystal optical element 101 to increase the depth of focus. A high resolution pattern image is obtained.

The fact that the image formation is telecentric in this embodiment means that the principal ray, which is the center of the image formation light beam, is perpendicular to the surface of the wafer 5 after passing through the projection optical system 3. ..

Since the crystal optical element 101 in this embodiment is arranged between the projection optical system 3 and the wafer 5, the chief ray is incident on the crystal optical element 101 vertically. Since the vertically incident light passes vertically as it is, there is no deviation between the principal rays of the light split into two.

Therefore, even if the crystal optical element is inserted, the image points of the two lights will not be displaced in the direction perpendicular to the optical axis of the projection optical system. The position of the image forming point of the light divided into two only causes a shift in the optical axis direction of the projection optical system.

As described above, by inserting the crystal optical element 101 as shown in FIG. 13, a double focus can be achieved without affecting the magnification or distortion which is the deviation in the direction perpendicular to the optical axis direction. There is.

In this embodiment, the shift amount of the focus position of the projection optical system can be arbitrarily controlled by the thickness d of the crystal optical element as in the first embodiment. If the crystal optical elements having several kinds of thicknesses can be replaced with each other, a shift amount according to the pattern can be generated. Further, since the double images are generated at the same time, the trouble of double exposure does not occur, so that it is possible to suppress the decrease in throughput.

In this embodiment, since the element having power such as the lens which constitutes the projection optical system is fixed, the crystal optical element 101 is replaced as shown in FIG. It is easy to return to the configuration. In the case of actually using crystal which is the easiest to use as the crystal optical element, the crystal may be thinner than the practical thickness. Therefore, actually, as shown in FIG. 13, the crystal plate 101a is attached to the reinforcing member 61 having a constant thickness, such as quartz or BK7, to manufacture. The crystal plate and the reinforcing member are bonded by vacuum bonding. FIG. 5 shows a crystal optical element thus produced.

When the crystal optical element is manufactured as described above,
In order to return to the normal projection optical system, it is necessary to replace the plane parallel plate having the same optical path length as the normal optical system including the reinforcing member for the optical system.

In this embodiment, as in the case of the first embodiment shown in FIG. 1, when the crystal optical element is used, there are optimum illumination conditions, and it may be necessary to change the illumination condition depending on whether the crystal optical element is inserted or not. As a method of changing the illumination condition in this case, that is, a method of changing σ, various known methods such as changing the diaphragm in the illumination system 1 by the switching mechanism 10 can be used.

Next, Examples 5 and 6 of FIGS. 14 and 15 will be described. In Example 5 of FIG. 14, the crystal optical element 101 is used.
Is attached to the reticle 2 side.

In this embodiment, the projection optical system 3 in this case is a telecentric system not only on the side of the wafer 5 but also on the side of the reticle 2 so as not to shift the image point. As a basic relationship of image formation, the vertical magnification is the square of the horizontal magnification, and considering the normally used 1/5 times reduction system, the thickness of the crystal 101 is 25 times that in the case of being inserted on the wafer side in Example 4. Can be

As described above, if crystal is used as a crystal and the wafer side has a control of the order of 0.1 mm, the reticle side has a large control amount of the order of mm, which is a process control. Is facilitated.

In Example 6 of FIG. 15, the crystal optical element 101 is used.
Is inserted in the projection optical system 3 at a position where the chief ray is parallel to the optical axis of the projection optical system 3. When the projection optical system is telecentric on the wafer side, such a portion may appear inside the projection optical system.

The crystal optical element of the present invention can be inserted in such a place. The thickness of the crystal in this case is determined by the paraxial magnification relationship between the insertion position and the imaging position,
Generally, thicker crystals than in Example 4 are required.

14 and 15, a parallel plane plate 8 replaceable with the crystal optical element 101 used in the present invention is prepared, but the optical thicknesses of the crystal 101 and the plane parallel plate 8 are the same. ..

In the present embodiment, in the actual exposure, by inserting the pattern information from the console of the projection optical system 3, the type and presence of insertion of the crystal optical element are instructed, and these elements are automatically set up. Done. The same applies to the illumination conditions.

Particularly, in the present invention, the image forming characteristics of the optical system can be changed without impairing the features of the projection optical system, and the depth of the optical system for an isolated pattern such as a contact hole can be increased. Is very effective.

[0101]

According to the present invention, the crystal optical element is inserted into a telecentric portion of the projection optical system, and when the crystal optical element shown in FIG. It achieves deep depth of focus imaging for the pattern.

In particular, in the present invention, in the case of exposure of a normal pattern, when the crystal optical element and the crystal optical element shown in FIG. 2 are used, the diaphragm is removed and the conditions of the illumination system and the like are set again, thereby exposing the exposure system. There is no loss of the original function. Further, since the crystal optical element and the diaphragm are not elements having optical power themselves, they are not required to have high positional accuracy at the time of switching, which is a great advantage in implementation.

Further, since the present invention effectively divides the light beam passing through the projection optical system into two parts, the power system parts of the two optical paths are all common. Therefore, the characteristics such as distortion caused by the manufacturing error are exactly the same for the two lights, and the habit peculiar to each projection lens is completely canceled. When combining two optical systems to achieve a double focus, distortion matching becomes a big problem, and the effect of the present invention is great.

Further, in the present invention, since two images are generated at the same time, exposure can be performed at the same time. Therefore, it is not necessary to operate the shutter every time the object to be exposed is moved in the optical axis direction of the projection optical system. Therefore, it is advantageous in terms of throughput, and since an error factor associated with movement can be removed, the stability of the entire system is improved.

Further, in the present invention, it is easy to replace the crystal optical element and the diaphragm. Therefore, by preparing a plurality of crystal optical elements and diaphragms, it is possible to select the one according to the characteristics of the projected pattern. It is possible to form an image according to the peculiarity of the pattern.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a projection exposure apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a crystal optical element used in the present invention.

FIG. 3 is an explanatory diagram of a light emission point when exiting a crystal optical element.

FIG. 4 is a diagram showing the propagation of light after exiting the crystal optical element.

FIG. 5 is a diagram showing the shape of a diaphragm.

FIG. 6 is a diagram showing an actual configuration of a crystal optical element.

FIG. 7 is a schematic view of the essential portions of Embodiment 2 of the projection exposure apparatus of the present invention.

FIG. 8 is a schematic view of the essential portions of Embodiment 3 of the projection exposure apparatus of the present invention.

FIG. 9 is a schematic view of the essential portions of Embodiment 4 of the projection exposure apparatus of the present invention.

FIG. 10 is a diagram showing light propagation in the crystal optical element used in the present invention.

FIG. 11 is a diagram showing a state in which light that has passed through the crystal optical element forms an image.

FIG. 12 is a graph showing the relationship between the angle of light incident on the crystal optical element and the shift of the image formation point.

FIG. 13 is a diagram showing an actual configuration of a crystal optical element.

FIG. 14 is a schematic view of the essential portions of Embodiment 5 of the projection exposure apparatus of the present invention.

FIG. 15 is a schematic view of the essential portions of Embodiment 6 of the projection exposure apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illumination system 2 Reticle 3 Projection optical system 4,101 Crystal optical element 5 Wafer 6 Wafer holding system 7 Cross diaphragm 8 Parallel plane plate 9 Circular diaphragm 10 Illumination condition switching mechanism

Claims (18)

[Claims] 1. When illuminating a circuit pattern on a first object plane with a light beam from an illumination system and projecting and exposing the circuit pattern on the first object plane onto a second object plane by a projection optical system, Two crystal optical elements whose optical axes are orthogonal to each other are arranged in the optical path between the first object and the second object, and a stop having a cross-shaped opening is provided near the pupil plane of the projection optical system. Is disposed so as to face the optical axis direction of the crystal optical element. 2. The direction of the optical axis of the crystal optical element and the cross-shaped opening direction of the diaphragm coincide with the main direction of the circuit pattern on the first object plane. Projection exposure device. 3. The projection exposure apparatus according to claim 1, wherein the projection optical system is a telecentric system on the second object side, and the two crystal optical elements are provided in the telecentric system. 4. A reticle and a wafer when a semiconductor device is manufactured by projecting and exposing a circuit pattern on a reticle surface illuminated by a light beam from an illumination system onto a wafer surface by a projection optical system and performing a developing process. Two crystal optical elements whose optical axes are orthogonal to each other are arranged in the optical path between the two, and a stop having a cross-shaped opening is provided in the vicinity of the pupil plane of the projection optical system. A method for manufacturing a semiconductor device, which is arranged so as to face the optical axis direction of the element. 5. The semiconductor device according to claim 4, wherein a direction of an optical axis of the crystal optical element and a cross-shaped opening direction of the diaphragm coincide with a main direction of a circuit pattern on the reticle surface. Manufacturing method. 6. The method of manufacturing a semiconductor device according to claim 4, wherein the projection optical system comprises a telecentric system on the wafer side, and the two crystal optical elements are provided in the telecentric system. 7. A circuit pattern on a first object plane is illuminated with a light beam from an illumination system, and when the circuit pattern on the first object plane is projected and exposed on a second object plane by a projection optical system, A crystal optical element is arranged in the optical path between the first object and the second object with its optical axis substantially aligned with the optical axis direction of the projection optical system, and a double focus is provided in the optical axis direction of the projection optical system. A projection exposure apparatus characterized by being formed. 8. When manufacturing a semiconductor device through a development processing step, projecting and exposing a circuit pattern on a reticle surface illuminated by a light beam from an illumination system onto a wafer surface by a projection optical system,
A crystal optical element is arranged in the optical path between the reticle and the wafer with its optical axis substantially aligned with the optical axis direction of the projection optical system, and a double focus is formed in the optical axis direction of the projection optical system. A method of manufacturing a semiconductor device, characterized in that. 9. A method of manufacturing a semiconductor device by projecting a circuit pattern onto a wafer by a projection optical system to print the circuit pattern on the wafer, and processing the wafer on which the circuit pattern is printed. , A plurality of images forming the circuit pattern at a plurality of positions in the optical axis direction of the projection optical system where the chief ray of each image forming light flux is substantially parallel to the optical axis of the projection optical system. A method of manufacturing a semiconductor device, which comprises disposing a refraction member. 10. The method of manufacturing a semiconductor device according to claim 9, wherein the circuit pattern is an isolated pattern such as a hole. 11. The method of manufacturing a semiconductor device according to claim 9, wherein the birefringent member comprises a single crystal plate, and the direction of the optical axis of the crystal plate is aligned with the direction of the optical axis. 12. The birefringent member includes first and second crystal plates, and optical axes of the first and second crystal plates are orthogonal to each other and are on a plane orthogonal to the optical axis. 10. The method for manufacturing a semiconductor device according to claim 9, wherein: 13. To block light that enters or passes through a portion corresponding to each quadrant when xy coordinates are set with the optical axis as the center and the directions of the respective optical axes are the directions of the x and y axes. 13. The method for manufacturing a semiconductor device according to claim 12, wherein the filter is provided. 14. A projection optical system for projecting a pattern of a mask onto a wafer, and a chief ray of each imaging light beam for imaging the pattern so as to image the pattern at a plurality of positions in the optical axis direction of the projection optical system. And a birefringent member disposed at a position substantially parallel to the optical axis of the projection optical system. 15. The projection exposure apparatus according to claim 14, wherein the birefringent member is provided so as to be retractable from the place. 16. The projection exposure apparatus according to claim 14, wherein the birefringent member comprises a single crystal plate, and the direction of the optical axis of the crystal plate is aligned with the direction of the optical axis. 17. The birefringent member includes first and second crystal plates, and optical axes of the first and second crystal plates are orthogonal to each other and are on a plane orthogonal to the optical axis. 15. The projection exposure apparatus according to claim 14, wherein the projection exposure apparatus is set as follows. 18. To block light that enters or passes through a portion corresponding to each quadrant when xy coordinates are set with the optical axis as the center and the directions of the respective optical axes are directions of the x and y axes. 18. The projection exposure apparatus according to claim 17, wherein the filter is provided.